This invention relates to rotary combustion engines of trochoidal type, and more particularly to a die-cast rotor housing having liquid cooling means for such engines.
In rotary engines of this type the pattern of heat flux is not uniform around the periphery of the engine, because each of the various phases of the engine cycle always takes place adjacent to the same portion of the housing. As a result, the peripheral shell in the region in which the combustion phase occurs has a much higher rate of heat input than other portions of the shell. This was recognized in U.S. Pat. No. 3,007,460 to Bentele, Jones, and Sollinger, issued Nov. 7, 1961. In that patent axial passages for flow of liquid coolant through the double-walled peripheral shell are provided, there being more of such passages in the circumferential zone wherein combustion occurs.
The inner wall of the peripheral shell requires a certain thickness at its side faces both radially inward and outward of the coolant passages for the provision of gasket grooves, and in the prior art this thickness was carried uniformly across the axial width of the shell, that is, the passages went straight through in the axial direction. It was not recognized that the pattern of heat flux also varies axially across the width of the shell, with the highest heat input at the midplane between the side walls. An inner wall of constant thickness makes no provision for this circumstance, with the result that the thickness required to accomodate the gaskets, when carried straight across, leaves the thickness at midplane too high to permit cooling at that point to the desired temperature of the working surface. Also, uneven cooling may cause distortions and occasional cracks, as well as undesirable wear and erosion of the inner surface.
In the copending U.S. application of Charles Jones, Ser. No. 489,825 filed July 18, 1974, now abandoned and having a common assignee with the present invention, provision is made for balanced heat removal from the shell in accordance with the axial pattern of heat flux, by making the inner wall of the shell in the region of high heat input thinner at the axial midplane of the shell than at its axial edges. That invention, however, contemplates only sandcasting of the shell, which is the conventional way of forming such elements of a rotary engine.
Sand-casting is a slow and relatively expensive mode of fabrication, and it is desirable to form the shell by means of diecasting, which would greatly increase production and lower costs. It has heretofore been impracticable to form by die-casting a peripheral shell of a rotary engine wherein the generally axial coolant passages are canted radially inwardly from their axial ends toward the midplane of the shell in order to reduce the inner wall thickness at that location. When a casting die is opened to discharge the product, the several parts of the die must each be retracted only in a straight line. Since the coolant passages of a peripheral shell are circumferentially disposed around the generally annular housing, and since the axial ends of such canted passages are disposed further radially outwardly than at the midplane of the shell, normal die-casting practice would require a die with a separately movable finger or slide from each side to form each passage, each such slide being retractable along its own axis. The cost of such a die and the associated mechanism for withdrawing each finger separately along a different line would be prohibitive and would more than offset the savings ordinarily realized by die-casting.
The present invention overcomes these difficulties.